The general objective of this project is the development of methods for the exposure of details of enzymic reactions by use of the heavy-atom kinetic isotope effect. Specific objectives for the next budget period are: 1) Completion of experimental and theoretical modeling work on the C13 isotope effects on the decarboxylation of malonic acid in water solution; 2) Completion of reaction coordinate eigenvector and reactant complexity studies on a simplified model of the enzyme-catalized decomposition of a pentatomic substance: 3) Initiation of computational studies of kinetic isotope effects in bond forming reactions. BIBLIOGRAPHIC REFERENCES: "Calculation of heavy-atom kinetic isotope effects: Application of the high temperature approximation to models with three-element reaction coordinates", by G.-J. Wei and Peter E. Yankwich, J. Chem. Phys., 62, 2200-2208 (1975). "Intermolecular C13 kinetic isotope effects in the decarboxylation of oxalic acid in dioxane solution", by Thomas T.-S. Huang, Richard W. Kidd, and Peter E. Yankwich, J. Chem. Phys., 62, 4757-4763 (1975).